Pneumatic tires typically have a circumferential rubber tread strip and said tread strip may be of cap/base layered construction. For said tread cap/base layered construction, the outer tread rubber cap layer contains a running surface (intended for ground-contacting) for the tire and the tread base layer underlies said tread rubber cap layer. Such tread cap/base layered construction is well known to those having a skill in such art.
In practice, said tread rubber cap layer may, in some instances, be comprised of an electrically insulating (poorly electrically conducting) rubber composition and said tread base layer comprised of a relatively electrically conductive rubber composition (relative to the rubber composition of said tread cap layer).
In such instance, it may be desired to provide a path of least electrical resistance between said tread rubber base layer through said outer tread cap layer to the running surface of said tread cap layer.
Numerous proposals have been made for providing a path of electrical resistance which extends though said electrically non-conductive outer tread rubber cap layer of a tire tread of a cap/base construction, such as, for example, a rubber strip of an electrically conductive rubber composition of the same rubber composition of and as an extension of an electrically conductive tread base layer rubber composition which underlies, and is substantially co-extensive with, said electrically non-conductive tread rubber cap layer. Exemplary of such proposals, which is not intended herein to be limited or all-inclusive, are, for example, U.S. Pat. No. 5,942,069.
For this invention, an improvement, which is intended to be a departure from such past practice, is an inclusion of an additional co-extruded, integral tread component of a specialized configuration which provides a path of least electrical resistance extending from said underlying tread base layer, through said outer tread cap layer to its running surface.
Said additional rubber tread component is of a circumferential inverted unitary “T” configuration comprised of a stem portion and a base portion, wherein its stem portion extends radially outward from its base portion through said outer tread cap rubber layer to said tread cap running surface, wherein its said base portion is positioned juxtapositioned to and underlies said tread cap rubber base layer and extends axially outwardly from both sides of said stem portion of said inverted “T” configured tread component to an extent less than the radial width of said tread cap layer.
Accordingly, a path of least electrical resistance is thereby provided which extends from the base of said additional inverted “T” configured tread component through said outer tread cap rubber layer to the running surface of said tread cap layer.
In practice the rubber composition of the tire tread rubber cap layer is electrically non conductive in a sense of containing a relatively minimal rubber reinforcing carbon black content (e.g. up to about 25 phr of rubber reinforcing carbon black) and the tire tread base layer and the said inverted “T” shaped tread component rubber composition extending through the tread cap is electrically more conductive (than said tread cap rubber composition) in a sense of having a more extensive rubber reinforcing carbon content (e.g. at least 40 phr of rubber reinforcing carbon black).
In the description of this invention, the term “phr” relates to parts by weight of an ingredient per 100 parts by weight of rubber, unless otherwise indicated.
The terms “rubber” and “elastomer” may be used interchangeably unless otherwise indicated. The terms “vulcanized” and “cured” may be used interchangeably unless otherwise indicated. The terms “compound” and “rubber composition” may be used interchangeably unless indicated. The term “carbon black” is used to refer to rubber reinforcing carbon blacks unless otherwise indicated. Exemplary rubber reinforcing carbon blacks may be referred to, for example, in the Vanderbilt Rubber Handbook (1978) on Pages 414 through 417.